The long term goal of this research is to extend our understanding of the basic processes underlying the development of autism, which will ultimately provide the basis for effective early identification &development of treatments focused on ameliorating the core aspects of the disorder. Building upon previous research on the importance of shared affect &imitation as fundamental to the autism phenotype, the present study will investigate low level imitative processes, typically termed mimicry, in children with autism relative to typically developing &developmental^ delayed children. It is still unclear to what extent mimicry is deficient in children with autism, whether it precedes more complex imitative problems &what mechanisms are involved. By investigating how emotional facial mimicry differs in those with autism compared to typically developing individuals &those with other developmental delays, the consequences of mimicry for development will be elucidated. This will provide a clearer sense of what processes are affected in this disorder &will allow focused treatments on those mechanisms which are still intact in those with autism. Three groups of children (with autism, typically developing and with non-autism developmental delays) will be exposed to several different videos and still photos while electromyographic readings are taken over the muscles responsible for mimicry of the stimuli. The stimuli will be varied on their emotional content, &will include both facial &bodily actions. This will reveal what those with autism do &do not mimic, &will differentiate possible mechanisms for the mimicry deficit seen those with autism. These data will be combined with longitudinal data that has been collected on a subgroup of these children &measures heir social functioning, communication skills, imitative abilities &severity of autism symptoms. The longitudinal data will be used to explain the variance of mimicry seen in this groups &may reveal subgroups of autism symptoms, potentially allowing prediction of ASD subtypes, &understanding of the broader autism phenotype. PUBLIC HEALTH RELEVANCE: Autism is a debilitating developmental social disorder that has emerged as a major public heath concern. Recent research suggests that 1 child in 166 (Fombonne, 2003) is affected by autism spectrum disorder (ASD). Currently, treatment of autism is expensive &difficult &may provide only partial remediation of the symptoms. That the basic mechanisms of this disorder are not well understood further complicates treatment as many paradigms focus on specific symptoms without addressing the underlying deficit.